Each year many people lose their lives in fires. The majority of these people are killed by high carbon monoxide levels or low oxygen levels rather than by the direct action of the fire itself.
Only about 1% of the homes in the U.S. have fire alarm systems. Where fire alarm systems are used, they are generally based on various heat sensing devices. These range from central systems having heat detectors strategically placed throughout a building to individual battery or gas operated devices which can be strategically located. Since these systems rely on heat sensing devices, smoldering fires are often undetected, thus allowing carbon monoxide and other combustion products to build up to toxic levels, i.e., levels causing people to lose consciousness and die.
Some types of fires are often associated with very heavy smoke production. For example, smoldering carpets, upholstery, bedding and insulation can produce large quantities of smoke during the early stages of a fire. Lethal levels of carbon monoxide and other combustion products can quickly develop from such fires if they remain undetected.
There is a need for an inexpensive, reliable system for alerting people to the presence of smoke. The word smoke as used herein is intended to include both toxic gases and suspended, particulate matter. The alerting system also needs to be simple, maintenance-free and have a long, useful life.
In addition to alerting people to smoke hazards, the alarm chemicals can be incorporated into materials which may be accidentally subjected to excessive heat. Thus they can be incorporated into electrical cables, TV on-off switches, heating pads and the like. These substrates are occasionally exposed to excessive heat, and when this occurs, the alarm chemicals will be released thereby warning people of the hazard.